The present invention relates to visual display devices and, more particularly, to a composite integrated LED (light-emitting diode) display array, the LED devices being in planar array in a monolithic crystal wherein light is generated at a back surface of the crystal but transmitted through it and observed from the front surface of the crystal.
Heretofore, semiconductor light-emitting devices (whether of discrete, matrix, or array types) have been utilized in a fashion in which light was generated at or close to a "front" surface which is viewed by the observer. It has recently been proposed to construct LED devices from a transparent crystal in which light is generated at the "back" surface of the crystal but is transmitted through it and viewed from the "front" of the crystal. It is herein proposed to utilize this concept in a composite semiconductor array which includes an integrated circuit. The array disclosed is of an X-Y addressable configuration, i.e., a solid state planar array.
In the past, a variet of devices for non-permanent visual presentation of information has been available. Perhaps one of the most widely used and accepted visual display devices is the cathode ray tube. While the cathode ray tube has served admirably in many dieverse applications, it does suffer many disadvantages which limits its future use in many applications. These include high-voltage requirements (usually of the order of 15,000 volts or more) and x-ray and radio frequency emissions which are attendant to such high voltages requiring shielding in order to reduce radio-frequency interference. In addition, cathode ray tubes are expensive owing to their complexity of manufacture and their relatively short lifetime requireing periodic replacement. The low light output of cathode tube displays requires care to prevent glare from the ambient surroundings from preventing the readability of the display. Even under ideal conditions, cathode ray tube displays being analog in nature have poor resolution with accuracies achievable only to about 2%. Furthermore, the large size and weight and the nonruggedness of the cathode ray displays prevent their use in many environments where space is at a premium and rugged, dependable construction is a prerequisite.
Another type of display is the so-called plasma discharge (or simply "gas discharge") display, in which gas between planar electrodes in a gas-filled envelope is excited by voltages across the electrodes provides emission of light. Such devices require relatively high energizing voltages, are somewhat bulky, and have limited lifetime. Because of their higher energizing voltages, they are not directly compatible with semiconductor circuitry of the type employed in integrated circuits.
These and other type of displays are described, and their relative merits noted, in the article entitle "Circuit/System Building Blocks" by Lapidus, G., in IEEE Spectrum, Vol. 11, No. 1, January, 1974, p. 54.
Recently, semiconductor light-emitting diodes ("LED's") and other semiconductor light-emitting devices have been developed. While LED's were predicted to lend themselves to fabrication in a form amenable to X-Y scanning, a simple X-Y matrix of solid-state light-emitting devices has many drawbacks. One major disadvantage to X-Y scanning of a large array is that high-peak currents are required for very short periods of time. Further, where a large number of LED's are simply arrayed, as in the form of an integrated semiconductor display chip, optical crosstalk often occurs, i.e., a manifestation in which an LED which is energized scatters light to adjacent non-energized LED's, making the latter appear to be energized, or reducing the contrast, resolution and general optical quality of any image displayed by the array. Moreover, the use of LED's in a multicolor display array presents formidable problems, particularly as to the difficulties of providing electrical interconnection between electronic circuit elements (e.g., memory and drive circuits) and the individual LED's. Prior art approaches have not satisfactorily solved such problems and have not facilitated the desirable integration of the display array with integrated circuitry for energizing the LED's.